Just before they begin three series against the best the National League has to offer -- St. Louis, Atlanta and Florida -- the slumping Washington Nationals shook up their pitching staff yesterday, sending struggling right-handers Zach Day and Claudio Vargas to the minors, placing reliever Jon Rauch on the disabled list with a shoulder injury that could end his season and signing journeyman left-hander C.J. Nitkowski, released earlier in the day by the Pittsburgh Pirates.

The changes, necessitated both by injury and performance, come a day after the Cincinnati Reds, one of the league's worst teams, handed the Nationals their first three-game sweep of the season, making it five losses in the first six games of their current road trip and leaving them just one game over .500.

"I don't like to lose," Nationals General Manager Jim Bowden said by phone. "I don't like this road trip. I don't like losing to teams we're better than.

"Look, we've got 10 guys on the disabled list, more than any other team. But we need to fix the parts that are broken, and remind people that if they don't perform, they're out of here, and we'll get someone else in."

To complete the frantic day, the Nationals also activated reliever T.J. Tucker, on the disabled list since April 20 with a groin strain, from his rehabilitation assignment at Class AAA New Orleans and recalled right-hander Sun Woo Kim and outfielder Tyrell Godwin from New Orleans. Outfielder Terrmel Sledge, who is almost certainly lost for the season with a hamstring pull, was moved from the 15- to the 60-day disabled list.

The addition of Nitkowski -- 18-32 with a 5.35 ERA in 329 major league appearances -- potentially gives the Nationals a weapon they haven't had since lefty Joey Eischen broke his right arm May 1. Though right-hander Gary Majewski is holding left-handed hitters to a .125 average, Nitkowski, 32, could be valuable against such Cardinals as Jim Edmonds and Larry Walker.

Nitkowski had been pitching for Pittsburgh's Class AAA affiliate, Indianapolis, where he posted a 0.83 ERA in 19 appearances. He will earn a prorated salary of $400,000 as long as he's in the majors with the Nationals.

"I don't know what we'll get from this guy," Bowden said. "Maybe he's figured out how to get lefties out. . . . [Manager] Frank [Robinson] should have all the weapons he needs against the Cardinals."

Of all the moves, perhaps the most notable was Day's demotion. After securing the fifth starter's spot in spring training, he struggled, losing his turn in the rotation to John Patterson and subsequently failing to adjust to the bullpen. Asked this week how Day had handled his change in roles, Robinson said, "Not well."

The nadir for Day -- who is 1-2 with a 6.75 ERA -- came in a May 3 start against the Los Angeles Dodgers, when Robinson removed him with one out in the fourth inning even though just two runs had scored. Day turned his back to Robinson, and each man later acknowledged that Day might benefit from a trade to another organization.

Bowden, however, has been reluctant to do that -- in part because Day's performance wouldn't yield a worthwhile return and he believes Day has the talent to be successful in Washington. In Wednesday's blowout loss to the Reds, Day allowed five runs in two innings.

"He's not going to get any better sitting in the bullpen," Bowden said. "He's shown us that. We need to fix him and get him right, and we're not going to be able to fix it the way he's going up here. He's too important to let go."

The decision on Vargas, who is 0-3 with a 9.24 ERA in four starts, was easier. Though he throws a fastball in the mid-90s, Nationals executives don't value him as much as Day, Patterson or other young pitchers. Vargas lasted just 1 2/3 innings Wednesday.

Rauch's injury came to light in his appearance Wednesday against Cincinnati, when he allowed three runs in 3 1/3 innings. He had an MRI after the game.

"It's probably been developing for a while," team physician Bruce Thomas said. "He was throwing hard, and then he just couldn't. A small tear probably just gave way."

Thomas said if the tear is small and doctors are able to repair it easily, Rauch could return by the end of the season. "I've seen that," Thomas said. "But I've also seen plenty of times where it's bad enough that he would have to aim to be ready by next spring."

Tucker pitched four innings of scoreless ball in two appearances for New Orleans, and Kim (4-2 with a 2.76 ERA) has been the Zephyrs' best starter and made 43 appearances for the Montreal Expos last year. He'll likely be used in a mop-up role.

The club would rather not promote Godwin, despite his .333 average, .394 on-base percentage and 11 stolen bases, because they feel he needs to play every day to develop. He's the most likely candidate to be sent down when Patterson, placed on the disabled list Wednesday with back problems, is activated to start next Tuesday against Atlanta.